While it has a 1975 publication date and indeed most of it does appear to be of that vintage, note that several pages have "revisions" dating to 1976 and the few pages near the end have even later dates: Birdie's entry is dated 9/1/80 and CosMc -- a character I distinctly remember from my late-1980s childhood being introduced (and quickly vanishing) -- has a 10/88 date.

It makes me wonder if there are even more revisions/additions out there not included in this collection.